The present invention relates to room temperature curable epoxy coatings, particularly to room temperature curable epoxy compositions for forming thick protective cement coatings on substrates such as steel and concrete. Resinous epoxides are reacted with primary and secondary amines to provide such materials as adhesives, films, cements, floor toppings, highway surfacings, impregnated products such as fiberglass reinforced epoxy laminates and the like.
Epoxy cement compositions ae widely used as protective surfacers on concrete and steel substrates such as walls, ceilings, and floors, reactors, storage tanks, etc. which are exposed to corrosive chemicals. Such surfacer cements usually include inorganic fillers such as finely divided silica and graded silica sand, and are applied in thick coatings of from about 1 to 15 millimeters in thickness.
Room temperature cured chemically resistant epoxy compositions are described in U.S. Pat. No. 3,794,609 to Metil, assigned to the assignee of the present application. The disclosure of the Metil patent is incorporated herein by this reference. The patent describes epoxy compositions comprising resinous epoxide, polyfunctional organic solid amine effective alone as a high temperature curing agent for resinous epoxide, and a solvent for the curing agent which modifies the action of the curing agent to provide room temperature curing. Exemplary amine curing agents are aromatic amines such as metaphenylene diamine, p,p'-methylene dianiline, p,p'-diaminodiphenyl oxide, and other cyclic amino substituted compounds. Such compositions have a reasonable pot or working life, for example, 21/2 to 31/2 hours, and a reasonable setting time, for example, 8 to 48 hours. Such compositions cure by chemical reaction rather than by release of solvent and hence can be used in a very thick coatings.
U.S. Pat. No. 3,291,775 to Holm, the disclosure of which is incorporated herein by this reference, describes room temperature curing epoxide compositions comprising resinous epoxide and ketimine curing agents. The ketimine curing agents are reaction products of polyamine curing agents and ketones or aldehydes. Such compositions are stable in the absence of moisture but when exposed to moisture, for example, when coated on a substrate exposed to moist air, the compositions absorb moisture. The ketimine groups of the curing agents react with the absorbed moisture to form free amine groups, which then react with the epoxide groups to cure the composition. The described compositions are not desirable as cement surfacer composition because they depend for cure upon absorption of moisture from the atmosphere. Thin films on the order of 0.05 to 0.5 millimeter thick will cure at a reasonable rate by absorption of moisture from the atmosphere. However, such compositions would cure much too slowly, if at all, when applied in thick coatings such as films from about 1 to 15 millimeters in thickness. Moreover, the use of ketimine curing agents alone may not, depending upon the content of inorganic filler, if any, in the composition, provide a composition having sufficient body during its working life for application in thick, sag-free coatings to substantially vertical surfaces. The patent also discloses that in addition to ketimines, accelerators such as water and aliphatic polyamines in minor amounts up to about 3% based on the polyimine curing agent may be employed.
Other ketimine curing agents for epoxy resins are described in U.S. Pat. Nos. 3,386,953, 3,432,574, 3,442,856, 3,401,146 and 3,397,178. U.S. Pat. No. 3,337,606 to Floyd describes epoxy compositions containing long chain aliphatic curing agents having a ketimine group and a nitrile group, and states that water may be included in such compositions to accelerate cure. Example IX of the patent shows water used in stoichiometric proportion to the ketamine group. However, although the curing agents described in the Floyd patent are said to give tough, flexible epoxy coatings, they are not desirable for preparing epoxy cement surfacer compositions that must have high resistance and attack by solvents and corrosive chemicals and high mechanical strength when applied in thick coatings.